It is generally known to dispense material at low feed rates. Many low feed rate applications typically require accurate and precise dispensing of material; for example, pharmaceuticals, cosmetics, dietary and nutrition products, chemical compositions, or the like. Such applications typically use batch feeder systems for their accuracy and precision. However, such batch systems are slow compared to other types of dispensing systems such as continuous dispensing systems.
It is also generally known to continuously dispense material by controlling the feed rate by monitoring or measuring weight of material in a hopper, which are generally referred to as gravimetric or loss-in-weight dispensing system. Such known gravimetric dispensing systems typically include a hopper supported on a scale, one or more weight sensors to measure the weight of the hopper, and a feeder to move material from the hopper to a discharge chute. The weight of the empty hopper may be counterbalanced by a dead weight so that the weight sensor only detects the weight of material within the hopper. However, such known gravimetric dispensing systems have several disadvantages. For example, typical gravimetric systems are designed to dispense large amounts of material and not to precisely dispense small amounts of material. Also, the location of the weight sensor in known dispensing systems results in inaccurate measurements of the total weight of material in the hopper when shifted material does not cause a force to be applied to the weight sensor. Known systems may try to compensate for shifting loads by using an accelerometer or an electronic filters of one kind or another; however, the use of such electronics tends to decrease the accuracy and speed of measurement. For example, U.S. Pat. No. 4,722,456 describes a loss-in-weight feeding system including a weight sensing system having a balance assembly, a weight sensor, and an accelerometer. The accelerometer is mounted on a beam close to the position of the weight sensor and is specifically described as being sufficiently remote from the main fulcrum.
Accordingly, it would be advantageous to provide a dispensing system that could continuously and precisely dispense material at low feed rates. It would also be advantageous to provide a dispensing system that has multiple weight sensors that more accurately measure the weight of material within the hopper under a variety of material configuration conditions. It would further be advantageous to provide a dispensing system that uses two or more load cells, particularly one large capacity load cell located at the pivot point of a counterbalanced scale and one low capacity load cell located at the hopper. It would further be advantageous to provide a counterbalanced weight sensing system applicable in a variety of applications including dry material feeders, bulk solid metering, loading or unloading trucks, trailers, railcars, and the like. It would be desirable to provide for a counterbalanced dispensing system with multiple load cells having one or more of these or other advantageous features. To provide an inexpensive, reliable, and widely adaptable counterbalanced dispensing system with multiple load cells that avoids the above-referenced and other problems would represent a significant advance in the art.